CHINESE JOURNAL OF PHYSICS VOL. 39, NO. 1 FEBRUARY 2001

Critical Point of Magnetic Nanostructures in the Ising Model

Huai-Yu Wang¹, Yun-Song Zhou², Enge Wang³ and D. L. Lin<sup>4

1</sup>Department of Physics, Yantai University, Yantai 264005* and

Central Iron and Steel Institute, Beijing, 100081, China

²Department of Physics, Capital Normal University, Beijing 100037, China

³Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

⁴Department of Physics, State University of New York at Buffalo, NY 14260-1500, U.S.A.
(Received October 17, 2000)

The critical temperature T_c of magnetic nanostructures is calculated by the variational cumulant expansion in the Ising model. Structures of column, plate and cubic shapes are constructed for the study of shape effects. It is found that T_c increases with the decreasing surface to volume ratio. The dependence of T_c on the growth direction is also studied for various cubic lattices.

PACS. 75.75.+a - Magnetic properties of nanostructures.
PACS. 75.30.-m - Intrinsic properties of magnetically ordered materials.
PACS. 64.70.-p $\;$- Specific phase transitions.

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